PDF(Pubmed)
Abstract：
The apextrin C-terminal (ApeC) domain is a class of newly discovered protein domains with an origin dating back to prokaryotes. ApeC-containing proteins (ACPs) have been found in various marine and aquatic invertebrates, but their functions and the underlying mechanisms are largely unknown. Early studies suggested that amphioxus ACP1 and ACP2 bind to bacterial cell walls and have a role in immunity. Here we identified another two amphioxus ACPs (ACP3 and ACP5), which belong to the same phylogenetic clade with ACP1/2, but show distinct expression patterns and sequence divergence (40-50% sequence identities). Both ACP3 and ACP5 were mainly expressed in the intestine and hepatic cecum, and could be up-regulated after bacterial challenge. Both prokaryotic-expressed recombinant ACP3 and ACP5 could bind with several species of bacteria and yeasts, showing agglutinating activity but no microbicidal activity. ELISA assays suggested that their ApeC domains could interact with peptidoglycan (PGN), but not with lipoteichoic acid (LTA), lipopolysaccharides (LPS) and zymosan A. Furthermore, they can only bind to Lys-type PGN from Staphylococcus aureus, but not to DAP-type PGN from Bacillus subtilis and not to moieties of PGN such as MDPs, NAMs and NAGs. This recognition spectrum is different from that of ACP1/2. We also found that when expressed in mammalian cells, ACP3 could interact with TRAF6 via a conserved non-ApeC region, which inhibited the ubiquitination of TRAF6 and hence suppressed downstream NF-κB activation. This work helped define a novel subfamily of ACPs, which have conserved structures, and have related yet diversified molecular functions. Its members have dual roles, with ApeC as a lectin and a conserved unknown region as a signal transduction regulator. These findings expand our understanding of the ACP functions and may guide future research on the role of ACPs in different animal clades.
摘要：
ApextrinC末端（ApeC）结构域是一类新发现的蛋白质结构域，其起源可追溯到原核生物。已在各种海洋和水生无脊椎动物中发现了含ApeC的蛋白质（ACP），但是它们的功能和潜在机制在很大程度上是未知的。早期研究表明，文昌鱼ACP1和ACP2与细菌细胞壁结合，在免疫中起作用。在这里，我们确定了另外两个文昌鱼ACP（ACP3和ACP5），与ACP1/2属于相同的系统发育进化枝，但显示出不同的表达模式和序列差异（40-50％的序列同一性）。ACP3和ACP5主要在肠和肝盲肠中表达，并可能在细菌攻击后上调。原核表达的重组ACP3和ACP5都能与几种细菌和酵母结合，显示凝集活性，但没有杀微生物活性。ELISA分析表明，它们的ApeC结构域可以与肽聚糖（PGN）相互作用，但不与脂磷壁酸（LTA），脂多糖（LPS）和酵母聚糖A。此外，它们只能与金黄色葡萄球菌的Lys型PGN结合，但不是来自枯草芽孢杆菌的DAP型PGN，也不是PGN的部分，如MDP，NAM和NAG。该识别光谱不同于ACP1/2的识别光谱。我们还发现，当在哺乳动物细胞中表达时，ACP3可以通过保守的非ApeC区域与TRAF6相互作用，抑制TRAF6的泛素化，从而抑制下游NF-κB激活。这项工作有助于定义一个新的ACP亚家族，具有保守的结构，并具有相关但多样化的分子功能。它的成员有双重角色，以ApeC为凝集素，保守的未知区域为信号转导调节因子。这些发现扩展了我们对ACP功能的理解，并可能指导未来对ACP在不同动物分化中的作用的研究。
